In the early hours of last Wednesday, footage appeared online purporting to show a chemical attack on Ghouta, an area held by rebels opposing the Syrian government. Harrowing eye-witness accounts and images of supposed delivery rockets followed.

Advertisement

UN weapons inspectors have now gained access to the area and are gathering samples for analysis and interviewing survivors. But how do we know it was sarin and what can science tell us about what should be done next?

The Syrian government is believed to have stockpiles of sarin, as well as mustard gas. Allegations of chemical attacks by both sides in Syria’s two-year civil war began last year. Until now, none had been convincing&colon; all had too few victims, with inappropriate symptoms and conflicting stories.

Last week’s attack was different. Hundreds of people are thought to have died, with many more affected. Weapons experts call sarin the most likely culprit as victims in the footage show telltale signs of nerve agent but not, for example, the burns caused by mustard gas. What’s more, medical personnel were contaminated while tending victims, points out Charles Blair, an expert in weapons of mass destruction at the Federation of American Scientists, as was the case in the 1995 sarin attack in Tokyo.

Sarin kills by blocking the breakdown of acetylcholine, which transmits signals from nerves to muscles. This causes muscles to spasm – including respiratory muscles. Jean-Pascal Zanders, formerly of the European Union Institute of Security Studies in Paris, sees evidence of sarin exposure in images from Damascus&colon; animals dead in the streets, and convulsing humans with pinpoint pupils and the red and blue discolouration of asphyxiation.

So if the agent was sarin, the UN inspectors now in Syria should find it, or its unique breakdown products, in people and the environment. Traces persisted for years at Halabja, the Iraqi town attacked with chemicals including sarin in 1988, says Blair. Knowing this will inform what the future holds for survivors (see “Iraq offers grim lessons for Syrian gas survivors“).

Who was responsible for launching the attack is another matter. The short-range rockets used to deliver it might provide clues. The inspectors will try to find and sample these, says Richard Guthrie, a chemical weapons specialist formerly with the Stockholm International Peace Research Institute in Sweden. They cannot address who launched them as this isn’t in their mandate, but if you have a rocket with a 2-kilometre range, and you know where it landed, you can estimate where it came from, says Guthrie.

There are already some clues. He notes that the day of the attack was the one day that week when the wind blew from government-held central Damascus towards the rebel-held eastern suburbs. That and the apparent lack of army casualties suggest government involvement.

So can the West take any action to prevent more attacks? The US has in the past bombed chemical weapons stockpiles, and US destroyers are in range. But a low-intensity explosion, Guthrie says, will release chemicals, and some stockpiles could well be in populated areas. A high-energy blast still won’t incinerate all the chemicals but it will lift any intact agents high up where they can spread hundreds of kilometres. Both types of strike are likely to kill people in the vicinity.